1. The Field of the Invention
This invention relates to a novel polymer composition and a resist composition containing the same. More particularly, this invention relates to a novel polymer applicable to the fabrication of a resist composition useful for MEMS (Micro Electro Mechanical Systems) using a variety of radiations, including far-infrared radiation (e.g., KrF Excimer laser, ArF Excimer laser, F2 Excimer laser, etc.), X-ray (e.g., synchrotron radiation), and charged particle beams (e.g., e-beam), and a resist composition containing the polymer.
2. Related Prior Art
With the progress of high-integration semiconductor devices, there has been a demand for an extra fine pattern of less than 0.2 micron in the manufacture of very LSI (Large-Scale Integration, VLSI) semiconductor products. Hence, the exposure wavelength becomes much shorter than the wavelength of the conventional radiations, such as g- or i-beam, and researches on the lithography using far-ultraviolet radiation, KrF Excimer laser, ArF Excimer laser, F2 Excimer laser, X-ray, and e-beam have recently drawn considerable attention. The light sources most spotlighted in the next-generation lithography requiring a pattern of less than 0.10 micron are ArF Excimer laser and F2 Excimer laser.
The resist composition includes a component having an acid-liable function (hereinafter, referred to as “polymer”), a component generating acids under irradiation (hereinafter, referred to as “photoacid generator”), a solvent, and in some cases, a dissolution inhibitor, or a basic additive.
The polymer used as a principal ingredient of the resist composition is supposed to minimize the light absorption at the exposure wavelength. The chemically amplified resists conventionally used for the ArF Excimer laser that mostly include an acryl-based polymer as a principal ingredient are poor in dry plasma etching resistance due to an excess of oxygen atoms in the polymer. The reason is because the increase in the thickness of the resist pattern, which is required in compensating for the poor etching resistance, makes it difficult to mount the resist pattern upward stably on the substrate.
In an attempt to solve this problem, some resins containing a large number of alicyclic olefin groups have been exploited as a polymer used for the resists for ArF Excimer laser or F2 Excimer laser. Specific examples of the resin are an acrylate polymer containing isobornyl groups or adamantanyl groups, an olefin polymer comprising pure norbornene derivatives, maleic anhydride-cycloolefin polymer, etc.
More specifically, the acrylate polymer includes the polymer containing alicyclic groups disclosed in SPIE (1996, 2724, 334), and the maleic anhydride-cycloolefin polymer includes the polymer disclosed in SPIE (1996, 2724, 355).
The acrylate polymer shows a low light absorption, but it is inferior in etching resistance to aromatic compounds.
The maleic anhydride-cycloolefin polymer is superior in etching resistance to the acrylate polymer but inferior in verticality of the pattern due to its high light absorption at ArF Excimer laser wavelengths. In addition, the maleic anhydride monomer, which is liable to hydrolysis with water, results in poor storage stability of the resist prepared.
The polymer of the pure norbornene derivative demands the use of a metal catalyst, and its polymerized resin is too hard to exhibit excellent properties as a resist ingredient.
To solve this problem, a copolymer of acrylate polymer and olefin is prepared. An example of the preparation method includes substituting an olefin with a halogen compound or an electron-withdrawing group (e.g, such as halogen, nitrile, or trifluoromethyl), and synthesizing the corresponding polymer, as illustrated in the following Scheme 1. Another method includes introducing a functional group such as trifluoromethyl at the alpha-position of acrylate, and synthesizing the copolymer with olefin. The synthesis can be expressed as the following Scheme 2.

In the Scheme 1, X is halogen, or nitrile group (—CN); Y is hydrogen, or methyl; and n and m denote the repeat unit of the monomers.

In the Scheme 2, Z is trifluoromethyl or nitrile group (—CN); n and m denote the repeat unit of the monomers.
The Scheme 1 shows an example of the reaction that introduces a halogen atom or a nitrile group to an olefin so as to enhance the radical reactivity of the olefin. The Scheme 2 shows an example of the reaction that introduces a substituent at an alpha-position of the acrylate to activate the copolymerization reaction of olefin and acrylate.
As described above, the preparation of a copolymer from an acrylate and an olefin necessarily demands the introduction of functional groups for enhancing the radical reactivity to the acrylate or the olefin, causing a deterioration of the solubility in a general solvent due to the introduced functional group. In addition, the use of the copolymer obtained by introducing such functional groups for a resist composition results in a deterioration of resolution and an increase in the energy required for pattern resolution (i.e., deterioration of sensitivity).